1. Technical Field
The following description relates to one or more techniques for retrieving development agent from a developer holding surface that is a cylindrical surface parallel to a main scanning direction.
2. Related Art
A developer supply device has been known that includes a developer holding member (a development roller), an upstream developer transfer unit, and a downstream developer transfer unit.
The developer holding member is disposed to face an electrostatic latent image holding body (a photoconductive drum) in a predetermined development area. The developer holding member has a developer holding surface on which charged development agent is held and carried.
The upstream developer transfer unit has an upstream transfer surface. The upstream transfer surface is disposed to face the developer holding surface across a predetermined distance at an upstream side relative to the development area in a moving direction of the developer holding surface. The upstream developer transfer unit is configured to generate an upstream transfer electric field (an electric field for transferring the development agent carried on the upstream transfer surface from an upstream side to a downstream side in the moving direction of the developer holding member).
The downstream developer transfer unit has a downstream transfer surface. The downstream transfer surface is disposed to face the developer holding surface across a predetermined distance at a downstream side relative to the development area in the moving direction of the developer holding surface. The downstream developer transfer unit is configured to generate a downstream transfer electric field (an electric field for transferring the development agent carried on the downstream transfer surface from the upstream side to the downstream side in the moving direction of the developer holding member).
In the above configuration, an electric field for transferring the charged development agent from the upstream side to the downstream side in the moving direction of the developer holding member is generated in a space on each of the upstream transfer surface and the downstream transfer surface. Thereby, the development agent is transferred from the upstream side to the downstream side in the moving direction of the developer holding member, on each of the upstream transfer surface and the downstream transfer surface.
The development agent, transferred by the upstream developer transfer unit, faces the developer holding surface in a position where the upstream transfer surface faces the developer holding surface (a circumferential surface of the development roller). Thereby, the development agent adheres onto the developer holding surface. In other words, the development agent is held and carried on the developer holding surface.
A part of the development agent held on the developer holding surface is consumed in the development area where the part of the development agent is supplied for development of an electrostatic latent image. Namely, when reaching the development area, the part of the development agent held on the developer holding surface adheres onto positions corresponding to the electrostatic latent image formed on the electrostatic latent image holding surface that is a circumferential surface of the electrostatic latent image holding body).
The other remaining part of the development agent held on the developer holding surface, which remaining part has not adheres onto the electrostatic latent image holding surface (not been consumed in the development area), is retrieved by the downstream developer transfer unit, and transferred from the upstream side to the downstream side in the moving direction of the developer holding member (in a rotational direction of the development roller) on the downstream transfer surface.